1985 US 308QV GTS 308 misfire at 2500-3000 rpm | FerrariChat
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1985 US 308QV GTS 308 misfire at 2500-3000 rpm

Discussion in '308/328' started by jlc308, Sep 16, 2009.

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  1. jlc308

    jlc308 Karting

    Jul 11, 2009
    121
    Irvine CA
    #1 jlc308, Sep 16, 2009
    Hello to all, new to this great forum. Had my car for 12 years, 53,000 miles and I personally drove 2500 miles in 12 years. Always passed Calif smog until recently. Calif test requires to be dyno tested at 2500 rpm under and that is exactly where my misfire begins. This will result in high HC levels due to unburnt fuel. My own road test is driving on the highway and at approx 50 mph in 5th gear, 2500-3000rpm, it begins to misfire like a fouled plug. Take it up to 70, 80, 90, 100mph no problem, runs strong and smooth. Run the car from a standstill and go thru all 5 gears and hit 100 mph, no problem. So far I changed the following:

    Wires, Taylor 8mm spiro pro
    Extenders black made by Mafer Italian
    Dist caps
    rotors
    grounde both digiplexs
    replaced all 8 Bosch fuel injectrors
    remove, cleaned tested TDC sensors 720 ohm each
    new Bosch O2 protection relay
    new battery
    new Bosch O2 sensor
    gone two tanks of new gas
    idle is ok at about 1100 to 1200 rpm
    just ordered new rebuilt WUR
    Running out of options, could it be plugged catalytic converter, fuel mixture?

    help
     
  2. wazie7262

    wazie7262 Formula 3

    Feb 13, 2008
    2,357
    Temecula, CA
    Full Name:
    Scott
    #2 wazie7262, Sep 17, 2009
    I hope you mean 25,000 miles in 12 years, not the stated 2500.
     
  3. jlc308

    jlc308 Karting

    Jul 11, 2009
    121
    Irvine CA
    #3 jlc308, Sep 17, 2009
    yes, 2500 miles 200 per year
     
  4. barcheta

    barcheta F1 Rookie

    Nov 15, 2003
    3,738
    Maryland
    Full Name:
    Jim
    #4 barcheta, Sep 17, 2009
    Did you clean the grounds on the fuel injection ecu? Also make sure the main grounding strap is clean and free of corrosion. I'd also possibly take a look at the fuel distributor and see if you have any buildup in that since you use the car so infrequently.
     
  5. fdekeu

    fdekeu Formula Junior
    Silver Subscribed

    Jun 19, 2008
    631
    Belzium
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    Frank
    #5 fdekeu, Sep 17, 2009
    Hello jlc,

    I have exactly the same problem on my Mondial 3200 (no cat)
    misfire between 2500-3000rpm
    Have already posted here as well
    http://www.ferrarichat.com/forum/showthread.php?t=257063
    Have only tried:
    new plugs
    new rotors
    cleaned ecu ground
    Was looking at new plug wires
     
  6. climb

    climb F1 Rookie

    Sep 19, 2006
    4,866
    Atlantic Beach Fl
    Full Name:
    Stuart K. Hicks
    #6 climb, Sep 17, 2009
    Last edited: Sep 17, 2009
    Got the same problem (at warm temps only) on my '80 gtsi.

    I've:

    replaced plugs and wires

    replaced extenders

    new rotors, carbon bottons and springs

    new grounds from digiplex boxes.

    cleaned TDC and tach sensor connections.

    It's drivin' me nuts.

    If you haven't already you may check the ground from the coils. I have test pipes BTW.

    I'm thinking the solution is gonna end up being an electronic ignition.
     
  7. barcheta

    barcheta F1 Rookie

    Nov 15, 2003
    3,738
    Maryland
    Full Name:
    Jim
    #7 barcheta, Sep 17, 2009
    Climb and jlc, if all you've done is cleaned the crank sensors that might be your problem. I'm not suggesting you just throw money at it till you fix something but replacing the crank sensors with new ones may very well resolve the issues.
     
  8. spiderseeker

    spiderseeker Formula 3

    Jul 22, 2005
    1,718
    Colorado
    Full Name:
    Steve
    #8 spiderseeker, Sep 17, 2009
    2 things to try-

    1. 85' US 308qv's have RED extenders NOT black, there is a difference in resistance.

    2. make sure that the AAV is clean and moves freely, 1100-1200 is a little fast, 1000 rpm is normal at idle.
     
  9. jlc308

    jlc308 Karting

    Jul 11, 2009
    121
    Irvine CA
    #9 jlc308, Sep 17, 2009
    Thanks for all the replys, I'm glad I'm not alone. My extenders were black when I bought the car 12 years ago and it has run fine up until now. The black ones have no resistor( I took the old one apart to verify) I purchased the extenders from T Rutlands and returned them immediately because they were poor quality knockoffs possibly made in China. Beware and look closely at the material because the black casing had some type of metal composition which is perfect for arcing. I found new exact Italian extenders on ebay fortunately. I may have to replace the TDC sensors, there goes my hands again, but before I do that I will check the coil condition. Does anyone know what the coil readings should be?
     
  10. fdekeu

    fdekeu Formula Junior
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    Jun 19, 2008
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    Frank
    #10 fdekeu, Sep 19, 2009
    TDC sensors:
    119052
    Magneti Marelli Sen 8D on eBay uk for 20.5£
     
  11. fdekeu

    fdekeu Formula Junior
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    Jun 19, 2008
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    Frank
    #11 fdekeu, Apr 9, 2011
    Last edited: Apr 9, 2011
    Hi,

    I believe I have a solution to the misfire problems on some 3.0 and 3.2 engines
    Also on my 3.2 Mondial (Euro, no cat)
    The problem is that there is a misfire at low revs under load (e.g. in 5th gear under 3000rpm)
    I diagnosed it as being an air leak around an injector
    I poured water on top of the injectors and revved the engine
    In 2 places the water was sucked into the engine
    What happens is that the extra air causes a lean mixture in that cilinder and there is no ignition
    When the revs go up the amount of extra air is not sufficient to cause a lean mixture
    At idle or low load the underpressure is also limited and the problem does not occur

    In my car I have changed the O-rings of the injectors + added some sealant and the misfire is gone

    Regards,

    Frank
     
    climb likes this.
  12. jsa330

    jsa330 F1 World Champ
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    Oct 31, 2003
    10,046
    75225
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    Scott
    #12 jsa330, Apr 9, 2011
    My '83 GTS developed a backfiring problem late last year...intermittently yet predictably, the rpm at idle would drop followed by a loud bang, like a .22 cal. pistol makes.

    The ignition system for the rear cylider bank was missing a beat and expelling unburnt fuel throught the exhaust valves into the headers, where it would detonate.

    The problem was indeed a failing crank sensor, and installation of a new one solved the fuel detonation problem and has made the engine run allround better.
     

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